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CBSE Class 12 Math 2008 Solved Paper

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Question : 29 of 29
Marks: +1, -0
An insurance company insured 2000 scooter drivers, 4000 car drivers and 6000 truck drivers. The probability of an accident involving a scooter, a car and a truck are 0.01, 0.03 and 0.15 respectively. One of the insured persons meets with an accident. What is the probability that he is a scooter driver?
Solution:  
Let E1,E2E_1, E_2 and E3E_3 be the events of a driver being a scooter driver, car driver and truck driver respectively. Let A be the event that the person meets with an accident.
There are 2000 insured scooter drivers, 4000 insured car drivers and 6000 insured truck drivers.
Total number of insured vehicle drivers = 2000 + 4000 + 6000 = 12000
∴ P(E1)P(E_1) = 200012000\frac{2000}{12000} = 16\frac{1}{6} , P(E2)P(E_2) = 400012000\frac{4000}{12000} = 13\frac{1}{3} , P(E3)P(E_3) = 600012000\frac{6000}{12000} = 12\frac{1}{2}
Also, we have:
P (A|E1E_1) = 0.01 = 1100\frac{1}{100}
P (A|E2E_2) = 0.03 = 3100\frac{3}{100}
P (A|E3E_3) = 0.15 = 15100\frac{15}{100}
Now, the probability that the insured person who meets with an accident is a scooter driver is P (A|E1E_1).
Using Bayes’ theorem, we obtain:
P (E1E_1|A) =
P(E1)×P(A∣E1)P(E1)×P(A∣E1)+P(E2)×P(A∣E2)+P(E3)×P(A∣E3)\frac{P(E_1) \times P(A|E_1)}{P(E_1) \times P(A|E_1) + P(E_2) \times P(A|E_2) + P(E_3) \times P(A|E_3)}
= 16×110016×1100+13×3100+12×15100\frac{\frac{1}{6} \times \frac{1}{100}}{\frac{1}{6} \times \frac{1}{100} + \frac{1}{3} \times \frac{3}{100} + \frac{1}{2} \times \frac{15}{100}}
= 1616+1+152\frac{\frac{1}{6}}{\frac{1}{6} + 1 + \frac{15}{2}}
= 16×652\frac{1}{6} \times \frac{6}{52}
= 152\frac{1}{52}
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